We might be a long way from the Blower Bentleys of old, but the company has made a return to its sporting car roots in recent years. That means that they need to mix extreme ultra-luxury comfort with premium handling. And they do it with Bentley Dynamic Ride. Here’s how it works.
The tl;dr is that it’s a really fancy anti-roll bar. But this isn’t the place for a one-liner summary. This is for where you want to really understand just how it works.
So first we’ll need to cover the anti-roll bar (or the “stabilizer bar,” or “sway bar” depending on who you ask). Many names, one function. To stop the body of the vehicle from rolling in a curve, thereby keeping the suspension working in its proper operating range.
In its simplest form, it’s pretty much just a steel bar. Usually with a few bends in it. The bar is attached to the suspension on both sides of the axle. Left and right. It could be attached to the strut or the control arm, but it works the same either way. Finally, the bar is attached to the body or a subframe (which in turn is attached to the body or frame).
The bar will have a straight section – or mostly straight section – with an arm on each end. The length of the arm, and where it’s located on the suspension, decide how much force the bar exerts on suspension movement.
When both wheels move up or down at the same time – like when you hit a dip or a bump – the bar rotates in its body-mount bushings. In that case, the bar isn’t actually doing much. The wheels move up and down as if there was nothing there. When one wheel moves and the other doesn’t, that’s when the magic happens.
Turn left, and momentum leads to weight transfer to the right. That pushes the right-side suspension down and the body rolls. When it rolls, the left-side suspension moves in its travel too. Now, depending on how much suspension travel the car has, the tires are no longer parallel to the ground. Instead of using the car’s full contact patch, you’re only using part of it. And all that body roll is uncomfortable for passengers. Especially if the suspension compressed fully on the loaded up right side. Hit a bump and there’s nothing to absorb it except your butt.
With an anti-roll bar, when the right front wheel moves up and the left wheel moves down, the bar twists, like a spring. It takes a lot of force to twist a steel bar. Go ahead and try, we’ll wait.
The twisting force on the bar pushes back on the wheel that’s trying to move down. So it moves less. Both wheels stay closer to the middle of the car’s suspension travel. The car rolls less.
Automakers can use different thicknesses of bar, different attachment points, and different lengths of the arm that attaches to the suspension to modify how much stiffness, called roll stiffness, the bar adds.
The base model might have a bar half the diameter of the sporty version. Or if it’s in the rear of the car, none at all.
The problem with the anti-roll bar is that it’s attached to both wheels. I mean, that’s how it works, but it’s also the problem. See, when just one wheel moves, like hitting a bump, it puts a sudden force into the other side of the vehicle through the bar. In short, it rides more jarringly. It also limits how far one wheel can travel, relative to the one it’s attached to via the bar. The left side can’t droop or compress all the way unless the right side is doing the same thing.
So what if you could disconnect the bar on demand? That’d be perfect. What if you could do that in just 0.06 seconds? And for good measure, what if you could put your own force on the bar, instead of relying on the wheels moving? That’s Bentley Dynamic Ride.
Bentley stuck an electric motor in the middle of the bar. Since you can only get so much force out of a 48-volt electric motor (not enough), they added a planetary gear set like an automatic transmission to multiply the torque.
When the Bentleys that use the system, like the new Bentayga, corner, the computer adds torque to the bar thanks to the electric motor. Up to 959 lb-ft. If the body is rolling to the right, the motor twists to counter that, keeping it level, which is a big challenge in a 5,340 lb luxury SUV. It uses sensors that monitor steering angle, wheel position, and cornering forces.
On a smooth road, it can relax the bar. When a single wheel hits a bump, the opposite wheel isn’t affected. The computer can even exert an upward force on the wheel that’s hitting the bump. So instead of dropping into a pothole and smacking into the other side, the wheel lifts up and almost misses the bump completely.
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Even better for the new Bentayga, when the SUV goes off-road… Wait. Do drivers really take their $300k SUVs off-road? Well, Bentley thinks they do, so we’ll go with it. When the Bentayga takes to the rough stuff, the bar can be disconnected completely. That lets each wheel move as far as the air suspension will let it. So it can climb over rocks and logs without putting a wheel in the air (unless it’s a really big rock). Disconnecting the anti-roll bars makes the ride much more comfortable as well.
So that’s how Bentley’s Dynamic Ride can both improve ride comfort and benefit handling. The automaker says it’s the first 48-v active anti-roll bar. Though Lexus uses a 42-volt system to do something similar on the Land Cruiser, so it might be splitting, uh, wires, there a bit.